Allison 3000 & 4000 Gen 4 Fault Code: P0961 Pressure Control Solenoid Main Mod System Performance

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
Pressure control Main Mod solenoid is a normally closed solenoid used to modulate the transmission main pressure schedule. The Transmission Control Module (TCM) commands the solenoid ON when specific transmission and engine conditions are met. When the Main Mod solenoid is commanded ON, pressure is routed to the main regulator valve lowering the main pressure schedule. The TCM sends control current to the Main Mod solenoid from High Side Driver 1 (HSD1) via wire 111. HSD1 is continuously ON unless the TCM detects a fault condition. The TCM regulates the amount of current to the Main Mod solenoid by switching the Main Mod solenoid’s Low Side Driver ON and OFF. Wire 17 4 completes the circuit between the Main Mod solenoid and its Low Side Driver. DTC P0961 indicates that the TCM has detected continuous transmission clutch slip. To reduce engine loading, main pressure is reduced by Main Mod in N (Neutral), 1 (First Range), and 2 (Second Range) when engine speed is below 1500 rpm. When this DTC is active, full main pressure is commanded.

CONDITIONS FOR RUNNING THE DTC:
1. Hydraulic system is pressurized.
2. No shift in progress.
3. Hydraulic default condition not present.
4. Output speed is above 200 rpm.
5. Engine initialization or shutdown is not in process.

CONDITIONS FOR SETTING THE DTC:
DTC P0961 sets during steady-state condition when continuous transmission clutch slip is detected.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0961 is active, the following conditions will occur:
1. Full main pressure is commanded. Main Mod commanded OFF.
2. The CHECK TRANS light illuminates.
3. DTC is stored in the TCM history.
4. TCM inhibits TCC engagement.
5. TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
NOTE: This DTC requires Clutch Test using the diagnostic service too to detect clutch slip during a partial stall and also to pressurize clutches for measurement without needing to drive the vehicle. Note that main pressure and clutch pressures are reduced when the Main Mod Solenoid is energized. Low commanded Main Mod solenoid pressures shown in Data Monitor correlate to reduced main pressure and clutch pressures. Main pressure is reduced by Main Mod in N (Neutral), 1 (First Range), and 2 (Second Range) when engine speed is below 1500 rpm. Higher Main Mod commanded pressures correlate to no reduction in main pressure and clutch pressures. Refer to First Steps and Tips for Troubleshooting and the OEM Technician’s Library for more information about the action requests for Clutch Test, Full Main Pressure Test, and also the procedure for Stall Testing.

DTC P0961 may be caused by:
1. Output speed sensor signal circuit issues.
2. Turbine speed sensor signal circuit issues.
3. Low clutch pressures, main pressure, or control main pressure.
4. Control module issues like stuck/sticky valves, mechanically defective solenoids, broken springs, damaged valve bores, plugged suction filter, damaged gaskets, excessive leaks to exhaust, etc.
5. Transmission issues such as damaged output speed sensor wheel slot, worn and/or damaged seals or seal rings, dislocated snap rings, worn clutch packs, rotating drum damage (affecting turbine speed pickup), debris, excessive hydraulic circuit leaks to exhaust or other hydraulic circuits.

NOTE: Damage to the output speed sensor wheel slot is an indication the driveline does not meet ATI specifications. Correct all driveline issues before putting transmission back in service.

6. Issue with TCM.